Vertical beam tilt control antennas, which are capable of vertical (and/or horizontal) beam tilting, have recently been widely used as base station antennas in mobile communication systems due to many advantages.
Beam tilt schemes of vertical beam tilt control antennas can be largely divided into a mechanical beam tilt scheme and an electric beam tilt scheme. The mechanical beam tilt scheme is based on a manual or powered bracket structure provided at a portion coupled to a support pole in a conventional antenna. Operation of such a bracket structure varies the installation inclination of the antenna and enables the antenna's vertical beam tilt. The electric beam tilt scheme is based on multiple phase shifters and enables electric vertical beam tilt by varying the phase difference of signals supplied to respective antenna radiation elements arranged vertically. An example of technology related to such vertical beam tilt is disclosed in U.S. Pat. No. 6,864,837 of Donald L. Runyon et al. (entitled “VERTICAL ELECTRICAL DOWNTILT ANTENNA”, assigned to EMS Technologies, Inc., and issued on Mar. 8, 2005).
In addition, a technology has recently been developed which controls the antenna beam in the horizontal direction and thereby adjusts the sector aiming direction in conformity with the distribution of subscribers of the cell site. Horizontal control of the antenna beam can be conducted in two schemes, including an electric horizontal beam control scheme, which employs at least two columns of antennas and performs electric phase control of signals supplied to respective columns, and a control scheme which employs one column of antennas and horizontally moves them mechanically (steering).
When adjusting the horizontal aiming direction, furthermore, horizontal beam width variation is indispensable to suppress generation of shaded areas and minimize overlapping zones. As a technology for varying the horizontal beam width, there is a scheme which implements at least two rows of antennas in the horizontal direction and mechanically controls the horizontal aiming direction of reflection plates of respective rows so as to crisscross, thereby controlling the beam width. An example of such technology is disclosed in Korean Patent Application No. 2003-95761, entitled “MOBILE COMMUNICATION BASE STATION ANTENNA BEAM CONTROL APPARATUS”, filed by the present applicant.
As such, antennas for mobile communication systems have a request for a structure enabling vertical beam tilt adjustment, horizontal steering adjustment, and horizontal beam width control, as well as an increasing demand for formation of more optimized beam patterns for respective sectors, but application of such a structure requires that comparatively complicated, high-cost mechanical equipment be additionally employed, which could possibly make antenna characteristics unstable.